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INTRODUCTION TO ANIMAL DIVERSITY

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Title: INTRODUCTION TO ANIMAL DIVERSITY


1
INTRODUCTION TO ANIMAL DIVERSITY
  • Chapter 32
  • Our Kingdom
  • We are Animals

2
Animals Are
  • Species-rich
  • Morphologically diverse lineage of multicellular
    organisms on the tree of life
  • Distinguished by two traits
  • they eat
  • they move
  • The largest and most abundant predators,
    herbivores, and detritivores

3
Animals Are
  • Multicellular, heterotrophic eukaryotes
  • Heterotrophs
  • ingest food
  • find food by tunneling, swimming, filtering,
    crawling, creeping, slithering, walking, running,
    or flying.
  • Dominant consumers in both aquatic and
    terrestrial habitats
  • Animal cells lack cell walls
  • Distinguished by two tissues
  • Nervous tissue and muscle tissue
  • Most animals reproduce sexually with the diploid
    stage usually dominating the life cycle

4
Methods in the Study of Animals
  • Analyzing Comparative Morphology
  • The Evolution of Tissues
  • Symmetry and Cephalization
  • Evolution of a Body Cavity
  • The Protostome and Deuterostome Patterns of
    Development
  • The Tube-within-a-Tube Design
  • A Phylogeny of Animals Based on Morphology
  • Using the Fossil Record
  • Evaluating Molecular Phylogenies

5
Themes in the Diversification of Animals
  • Suspension (Filter) Feeding
  • Deposit Feeding
  • Herbivory
  • Predation
  • Parasitism
  • FeedingMovement
  • Types of Limbs Unjointed and Jointed
  • Are All Animal Appendages Homologous?
  • Reproduction and Life Cycles

6
Key Lineages of Animals
  • Choanoflagellates (Collar Flagellates)
  • Porifera (Sponges)
  • Cnidaria (Jellyfish, Corals, Anemones, Hydroids,
    Sea Fans)
  • Ctenophora (Comb Jellies)
  • Acoelomorpha

7
Monophyletic and Very Diverse
  • The animals are a monophyletic group
  • Animals are very diverse
  • 34 major animal phyla are recognized

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Analyzing Comparative Morphology
  • Most morphological diversity in animals is based
    on
  • differences in mouths and limbs

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Basic Architecture
  • Four features define an animal's body plan
  • the number of tissue types in embryos
  • the type of body symmetry
  • the presence or absence of a fluid-filled cavity
  • the way in which the earliest events of embryo
    development proceed

15
The Evolution of Tissues
  • All animals other than sponges have tissues
  • tightly integrated structural and functional
    units of cells.
  • Diploblasts
  • embryos have two types of tissues or germ layers
  • Ectoderm
  • Endoderm
  • Triploblasts
  • embryos have three types of tissues
  • Ectoderm
  • Endoderm
  • Mesoderm
  • germ layers develop into distinct adult tissues

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Symmetry and Cephalization
  • A basic feature of a multicellular body is the
    presence or absence of a plane of symmetry
  • radial symmetry
  • at least two planes of symmetry.
  • bilateral symmetry
  • a single plane of symmetry
  • face their environment in one direction.

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Cephalization
  • Bilateral symmetry allowed
  • Evolution of a head, or anterior region, where
    structures for feeding, sensing the environment,
    and processing information are concentrated

22
Evolution of a Body Cavity
  • Animals may or may not have an internal,
    fluid-filled body cavity
  • coelom
  • forms from within the mesoderm
  • lined with cells from the mesoderm

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Advantages of a Coelom
  • Creates a medium for circulation
  • Makes space for internal organs
  • A hydrostatic skeleton
  • fluid-filled chamber
  • allows movement
  • even without fins or limbs.

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The Protostome and Deuterostome Patterns of
Development
  • Coelomates are bilaterally symmetric
  • except echinoderms
  • three embryonic tissue layers
  • Bilatera
  • protostomes
  • arthropods, mollusks, and segmented worms
  • deuterostomes
  • vertebrates and echinoderms

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Differences in Early Development
  • Three events in early development differ in
    protostomes and deuterostomes
  • Cleavage
  • Gastrulation
  • coelom formation

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Cleavage
  • Rapid series of mitotic divisions
  • Spiral cleavage
  • mitotic spindles of dividing cells orient at an
    angle to the main axis of the cells
  • resulting in a helical arrangement
  • Radial cleavage
  • mitotic spindles of dividing cells orient
    parallel or perpendicular to the main axis of the
    cells
  • resulting in a pattern of cells stacked directly
    on top of each other

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The Tube-within-a-Tube Design
  • The basic animal body plan is a
    tube-within-a-tube design in which the outer tube
    forms the body wall and the inner tube forms the
    gut

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Ancestor?
  • The animal kingdom all developed from a common
    ancestor ( monophyletic) probable during the
    Precambrian era.


  • Probably a colonial choanoflagelate that lived
    about700 million years ago. Modern
    choanoflagellates are tiny, have a stalk and live
    in ponds and lakes)
  • A hypothesis of animal origin from flagellated
    protists says that the colony of cells in the
    protist evolved into a sphere and then
    differenciated and especialized creating two
    layers of cells.


36
The common ancestor of living animals
  • May have lived 1.2 billion800 million years ago
  • May have resembled modern choanoflagellates,
    protists that are the closest living relatives of
    animals

Figure 32.3
37
closest living relatives of animals
  • a colonial, flagellated protist

Figure 32.4
38
A Phylogeny of Animals Based on Morphology
  • The phylogenetic tree indicates that a group of
    protists called the choanoflagellates are the
    closest living relatives of animals and that the
    Porifera (sponges) are the most ancient animal
    phylum.

39
Phylogeny Based on Morphology
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  • Radially symmetric phyla are placed on the tree
    next because their tubelike body plans are
    relatively simple. Among the bilaterally
    symmetric phyla, the acoelomates and
    pseudocoelomates appeared first, followed by the
    coelomates.

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  • Two major events occurred after the coelomates
    split into the protostomes and deuterostomes
  • radial symmetry evolved
  • segmentation evolved independently in both
    lineages of coelomates.

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Using the Fossil Record
  • Most major groups of animals appear in the
    fossil record starting about 580 million years
    ago
  • The fossil record is generally consistent with
    the morphological phylogeny.

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Neoproterozoic Era (1 Billion524 Million Years
Ago)
  • Early members of the animal fossil record are
    known as the Ediacaran fauna( first fossils of
    animals about 575 mya). Simple radial forms and
    segmented bodies with legs.

Figure 32.5a, b
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Paleozoic Era (542251 Million Years Ago)
  • The Cambrian explosion marks the earliest fossil
    appearance of many major groups of living animals
  • Is described by several current hypotheses such
    as predator- prey relationships, oxygen increase
    and evolution of the hox genes

Figure 32.6
48
Mesozoic Era (25165.5 Million Years Ago)
  • During the Mesozoic era
  • Dinosaurs were the dominant terrestrial
    vertebrates
  • Coral reefs emerged, becoming important marine
    ecological niches for other organisms
  • The first mammals appeared (tiny, nocturnal
    insect eaters

49
Cenozoic Era (65.5 Million Years Ago to the
Present)
  • The beginning of this era
  • Followed mass extinctions of both terrestrial and
    marine animals
  • Modern mammal orders and insects
  • diversified during the Cenozoic
  • Also flowering plants appeared

50
Evaluating Molecular Phylogenies
  • The phylogenetic tree based on genes for
    ribosomal RNA and several proteins

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Points of Agreement
  • All animals share a common ancestor
  • Sponges are basal animals (branch from the base
    of tree, no tissues)
  • Eumetazoa is a clade of animals with true tissues
  • Most animal phyla belong to the clade Bilateria
  • Vertebrates belong to the clade Deuterostomia

53
Disagreement over the Bilaterians
  • The morphology-based tree
  • Divides the bilaterians into two clades
    deuterostomes and protostomes
  • In contrast, recent molecular studies
  • assign two sister taxa to the protostomes rather
    than one the ecdysozoans and the lophotrochozoans

54
Important Observations Emerge From the Data
  • The most ancient triploblasts lacked a coelom
  • The major event in the evolution of the Bilateria
    was the split between protostomes and
    deuterostomes
  • Segmentation evolved independently in the
    annelids and the arthropods and
  • Pseudocoeloms arose from coeloms twice in
    evolutionary history

55
Phylogenetic trees are best described as
  • true and inerrant statements about evolutionary
    relationships.
  • hypothetical portrayals of evolutionary
    relationships.
  • the most accurate possible representations of
    genetic relationships among taxa.
  • theories of evolution.
  • the closest things to absolute certainty that
    modern systematists can produce.

56
Themes in the Diversification of Animals
  • Within the phylum
  • basic features of the body plan do not vary from
    species to species
  • Diversity arose
  • mostly because of the evolution of innovative
    methods for feeding and moving

57
Feeding
  • The feeding tactics observed in animals can be
    broken into five general types
  • suspension feeding
  • deposit feeding
  • herbivory
  • predation
  • Parasitism
  • Many animals undergo a metamorphosis
  • a change in form during development
  • allows juveniles and adults to exploit different
    sources of food

58
Suspension (Filter) Feeding
  • Suspension feeders, or filter feeders, capture
    food by filtering out particles suspended in
    water or air
  • This method is found in a wide variety of animal
    groups and has evolved many times independently

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Deposit Feeding
  • Deposit feeders eat their way through a
    substrate
  • Food
  • soil-dwelling bacteria, protists, fungi, and
    archaea
  • detritusthe dead and partially decomposed
    remains of organisms
  • Depending on food
  • herbivores (plant eaters), parasites,
    detritivores (detritus eaters), or predators

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Herbivory
  • Herbivores
  • animals that digest algae or plant tissues
  • complex mouths with structures that make biting
    and chewing or sucking possible

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Predation
  • Sit-and-wait predators rarely move at all until
    prey is captured
  • stalkers pursue their prey

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Parasitism
  • Parasites are much smaller than their victims
    and often harvest nutrients without causing death
  • Endoparasites
  • live inside their hosts
  • often wormlike in shape
  • can be extremely simple morphologically
  • Ectoparasites
  • live outside their hosts
  • usually have grasping mouthparts
  • pierce the hosts exterior and suck the
    nutrient-rich fluids inside

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Movement
  • Many animals are sit-and-wait predators, and
    some are sessile throughout their adult lives.
    But the vast majority of animals move under their
    own power either as juveniles or as adults.

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Function of Movement
  • three functions in adult animals
  • Finding food
  • finding mates
  • escaping from predators.

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Limbs
  • A major innovation in animals
  • made highly controlled, rapid movement possible
  • Two types
  • Unjointed
  • saclike
  • Jointed
  • move when muscles that are attached to a skeleton
    contract or relax

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Homologous vs Non-Homologous
  • Biologists have argued that at least a few of
    the same genes are involved in the development of
    all appendages observed in animals
  • Hypothesis is that all animal appendages have
    some degree of genetic homology
  • that they are all derived from appendages that
    were present in a common ancestor.
  • This hypothesis is controversial, however, and
    research continues

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Reproduction and Life Cycles
  • At least some species in most animal phyla can
    reproduce asexually (via mitosis), as well as
    sexually (via meiosis).
  • Sexual reproduction can occur with internal or
    external fertilization

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Development
  • Eggs or embryos may be retained in the females
    body during development
  • viviparous
  • May be laid outside the body
  • oviparous
  • Female retains eggs inside her body during early
    development
  • embryos are nourished by yolk inside the egg and
    not by nutrients transferred directly from the
    mother
  • ovoviviparous
  • Vast majority of animals are oviparous

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Development
  • After a sperm fertilizes an egg
  • The zygote undergoes cleavage, leading to the
    formation of a blastula
  • The blastula undergoes gastrulation
  • Resulting in the formation of embryonic tissue
    layers and a gastrula

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.
  • Early embryonic development in animals

Figure 32.2
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Metamorphosis
  • The change from juvenile to adult body type
  • Larva
  • juvenile individual
  • looks substantially different from the adult
  • Nymph
  • juvenile individual
  • looks like a miniature adult

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Pupation
  • When a larva has grown sufficiently, it secretes
    a protective case and is now known as a pupa

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Into an Adult
  • During pupation, the pupas body is completely
    remodeled into a new, adult form

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Holometabolous
  • Complete metamorphosis
  • two-step process
  • from larva to pupa to adult
  • involving dramatic changes in morphology and
    habitat use

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Hemimetabolou
  • Incomplete metamorphosis
  • One-step process of sexual maturation.
  • Limited morphological difference between juvenile
    and adult

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Marine Animals
  • Complete metamorphosis
  • extremely common in marine animals
  • most cnidarians have two distinct body types
    during their life cycle
  • a largely sessile form called a polyp
  • alternates with a free-floating stage called a
    medusa

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